SECT, ii PHYSIOLOGY 173 



Myxomycetes (p. 54), plants, in spite of the great amount of water 

 contained in them, are of the nature of solid bodies. As such they 

 possess in common with inanimate objects the physical attributes of 

 weight, rigidity, elasticity, conductivity for light, heat, electricity, etc. 

 Important as these attributes are for the existence and continuance 

 of the life of a plant, they do not constitute that life itself. 



VITAL PHENOMENA ARE ESSENTIALLY BOUND UP WITH THE LIVING 

 PROTOPLASM. No other substance exhibits a similar series of remark- 

 able and varied phenomena, such as we may compare with the 

 attributes of life. As both physics and chemistry have been restricted 

 to the investigation of lifeless bodies, any attempt to explain vital 

 phenomena solely by chemical and physical laws could only 1>e induced 

 by a false conception of their real significance, and must lead to fruit- 

 less results. The physical attributes of air, water, and of the glasses 

 and metals made use of in physical apparatus, can never explain 

 qualities like nutrition, respiration, growth, irritability and repro- 

 duction. It would, indeed, be superfluous to emphasise the fact, were 

 it not that this error is from time to time repeated. 



The phenomena of life can only be studied and determined by the 

 most careful observation and critical examination of living organisms. 

 It is therefore necessary to establish what part the purely physical 

 and chemical properties which belong to all bodies, take in the 

 phenomena of life, and to what extent they are essential to the 

 maintenance of life itself. A perception of the strictly physical and 

 chemical processes going on within an organism is especially desirable, 

 though their exact determination is not more important than that of 

 the vital reactions, because operations are then involved with the 

 causes and effects of which we are already familiar. In questions 

 regarding strictly vital phenomena the case is quite different ; for it 

 then becomes impossible to predict what effect a particular cause will 

 produce. 



The free end of a horizontally extended flexible rod bends downwards merely 

 by its own weight. The same result will follow if any part of a dead plant, such 

 as a dry stem, be substituted for the rod. But if a living, growing stem be used 

 in the experiment, then the action of gravity will manifest itself in a manner 

 altogether at variance with its ordinary operation. That part of the stem which is 

 still in a state of growth will ultimately curve upwards, and BY ITS OWN ACTIVITY 

 ASSUME AN UPRIGHT POSITION ; it moves in a direction exactly contrary to the 

 attractive force of gravity. If a tap-root be similarly experimented upon, it will, 

 on the contrary, continue its downward movement until it places itself in a line 

 with the direction of the attraction ; a rhizome, however, under like circumstances, 

 would constantly maintain its growing apex in a horizontal position. In these 

 three experiments the force of gravity is exerted upon horizontal portions of 

 plants. The physical conditions are the same in each case, yet how entirely 

 different the results ! 



The explanation of this dissimilarity in the effects of the action 



